Method for performing metal injection with counter pressure

ABSTRACT

A system for metal injection and counter pressure has: a particle providing assembly; and a forming unit having a melting module, a counter pressure module and a mold module; wherein, the particle providing assembly provides particles with metal powder and a binding agent to the melting module, the particles are formed into melted flow by the melting module, the melted flow is provided to the mold module, the counter pressure module provides a counter gas with predetermined pressure to the mold module, the melted flow forms into a green part inside of the mold module.

FIELD OF THE INVENTION

The present invention relates to a system for metal injection and counter pressure and method using the same, and more particularly, to a system and method capable of applying a gas counter pressure onto its metallic injection material, as known as “feedstock”, for enabling the metal powder to be distributed uniformly so as to increase tensile strength while improving uneven shrinkage during sintering.

BACKGROUND OF THE INVENTION

Metal injection molding (MIM) offers a manufacturing capability for producing complex shapes in large quantities. The process utilizes fine metal powders which are custom formulated with a binder (various thermoplastics, waxes, and other materials) into a feedstock which is granulated and then fed into a cavity (or multiple cavities) of a conventional injection molding machine. After the “green” component is removed, most of the binder is extracted by thermal or solvent processing and the rest is removed as the component is sintered in a controlled-atmosphere furnace. The MIM process is used to produce relatively small, highly complex parts that otherwise would require extensive finish machining or assembly operations if made by any other metal-forming process. In addition, MIM parts can be treated with other subsequent metal conditioning treatments, such as annealing and surface finishing.

As with other injection molding processes and products, MIM also has its own set of disadvantages, including warpage deformation and shrinkage problems. Therefore, it is in need of methods and devices for overcoming those disadvantages.

SUMMARY OF THE INVENTION

In view of the disadvantages of prior art, the primary object of the present invention is to provide a metal injection system and method capable of applying a gas counter pressure onto its feedstock, such that not only is the feedstock compacted during feeding for improving tensile strength, but also the metal powders are enabled to be distributed uniformly in the feedstock so as to improve the uneven shrinkage problem caused during sintering.

To achieve the above object, the present invention provides a system for metal injection and counter pressure, which comprises:

-   -   a particle providing assembly; and     -   a forming unit, having a melting module, a counter pressure         module and a mold module;     -   wherein, the particle providing assembly provides particles with         metal powder and a binding agent to the melting module, the         particles are formed into a melted flow by the melting module,         the melted flow is provided to the mold module, the counter         pressure module provides a counter gas with a predetermined         pressure to the mold module, the melted flow forms into a green         part inside of the mold module.

The present invention provides a method for metal injection and counter pressure, which comprises the steps of:

-   -   providing particles; and     -   enabling a green part to be molded in a manner that the         particles are fed into a melting module for melting the         particles into a melted flow that is guided to flow into a mold         module while having a counter pressure module to apply a counter         gas with a predetermined pressure to the mold module during the         molding of the green part.

To sum up, during the molding of the green part by the use of the system and method of the present invention, the density of the green part is increased when there is a counter gas with the predetermined pressure being applied to the green part. In addition, not only is the feedstock compacted by the pressure of the counter gas and thus the tensile strength is enhanced, but also the metal powders in the feedstock are enabled to be distributed uniformly so that the uneven shrinkage problem caused during sintering is improved.

Further scope of applicability of the present application will become more apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from the detailed description given herein below and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention and wherein:

FIG. 1 is a schematic diagram showing a system for metal injection and counter pressure according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing a high-temperature gas module and a mold module in the present invention.

FIG. 3 a schematic diagram showing steps perform in a method for metal injection and counter pressure according to an embodiment of the present invention.

FIG. 4 is a schematic diagram density of different green parts.

FIG. 5 is a schematic diagram density of different green parts after debinding.

FIG. 6 is a schematic diagram density of different debinded green parts after sintering.

DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

For your esteemed members of reviewing committee to further understand and recognize the fulfilled functions and structural characteristics of the invention, several exemplary embodiments cooperating with detailed description are presented as the follows.

Please refer to FIG. 1, which is a schematic diagram showing a system for metal injection and counter pressure according to an embodiment of the present invention. In FIG. 1, a system for metal injection and counter pressure comprises: a mixing unit 10, a blending unit 11, a pulverizing unit 12, a granulation unit 13, a forming unit 14, a debinding unit 15, and a sintering unit 16.

The mixing unit 10 is used for mixing metal particles with a binding agent into a mixture. In this embodiment, the binding agent can be a mixture of paraffin and a polymer material or a polymer material, in which the polymer material can be polypropylene (PP). In addition, the amount of the metal particles in the mixture is about 50%˜70%, while preferably to be 55%, 60%, 65% or 70%; in a condition when the binding agent is a compound composed of paraffin and a polymer material, the amount of the polymer material in the compound is about 19%˜29%, while preferably to be 20%, 22%, 24%, 26% or 28%, and the amount of paraffin is about 11%˜21%, while preferably to be 12%, 14%, 16% or 18%. Nevertheless, the above description relating to the amount of binding agent and metal particles in the mixture is only for illustration and thus is not limited thereby.

Thereafter, the mixture is provided to the blending unit 11 where it is blended in a high temperature for enabling the binding agent to be distributed evenly on the surface of every metal particle so as to form a blend.

The blend is then provided to the pulverizing unit 12 for pulverizing the blend into a powder.

The granulation unit 13 is used for receiving the powder for processing the powder into particles. It is noted that the granulation unit 13, the pulverizing unit 12, the blending unit 11 and the mixing unit are generally being assembled together and treated as one particle providing assembly 17.

The forming unit 14 is composed of a melting module 140, a counter pressure module 141, a mold module 142 and a high-temperature gas module 143, in which the melting module 140 that is provided for receiving the particles is used for melting the particles into a melted flow while providing the melted flow to the mold module 142; the counter pressure module 141 is used for providing a counter gas to the mold module 142 while the melted flow is being solidified inside the mold module 142 into a green part.

Please refer to FIG. 2, which is a schematic diagram showing a high-temperature gas module and a mold module in the present invention. In this embodiment, the melt module 140 further comprises a feed nozzle 1400.

The mold module 142 is composed of a first half-mold 1420, a second half-mold 1421 and a mold temperature controller 1427.

The first half-mold 1420 is formed with a cavity 1422, at least one cavity temperature sensor 1425, at least one cavity pressure sensor 1424 and an air channel 1426, in which the cavity temperature sensor 1425 and the cavity pressure sensor 1424 are disposed inside the first half-mold 1420 at a position neighboring to the cavity 1422, and the air channel 1426 is connected to the cavity 1422.

The second half-mold 1421 is formed with a plunger channel 1423, at least one cavity pressure sensor 1424, and at least one cavity temperature sensor 1425, in which when the first half-mold 1421 is assembled with the second half-mold 1422, the plunger channel 1423 is disposed connecting to the cavity 1422, while allowing the feed nozzle 1400 to extend into the plunger channel 1423 for guiding the melted flow to flow into the cavity 1422.

The cavity pressure sensors 1424 are provided for detecting the pressure change inside the cavity 1422 to be used for controlling the timing for injecting the counter gas into the cavity 1422.

The cavity temperature sensors 1425 are connected to the mold temperature controller 1427, by that the temperature change inside the cavity 1422 can be detected and used for controlling the timing for injecting a high-temperature gas into the cavity 1422.

The counter pressure module 141 is composed of a counter gas source 1410, a compressor 1411, a high-pressure gas control valve 1412, a gas temperature sensor 1414, a controller 1415, and a first flow divider 1413. The counter gas source 1410 is connected to the compressor 1411 via a pipe for allowing the compressor 1411 to compress the gas from the counter gas source 1410. The compressor 1411 is further connected to the high-pressure gas control valve 1412 via a pipe, while the high-pressure gas control valve 1412 is connected to the gas temperature sensor 1414 and the first flow divider 1413. Moreover, the high-pressure gas control valve 1412 and the gas temperature sensor 1414 are connected to the controller 1415, by that the controller 1415 is enabled to receive gas temperature information from the gas temperature sensor 1414 and thus controls the openness of the high-pressure gas control valve 1412.

The high-temperature gas module 143 is composed of an air compressor 1430, an air dryer 1431, a flow meter 1432, a second flow divider 1433 and a heater 1434.

The air compressor 1430 is connected to the air dryer 1431 by a pipe for allowing the air dryer 1431 to dry the compressor air from the air compressor 1430. The flow meter 1432 is connected to the air dryer 1431 by a pipe for allowing the flow meter 1432 to measure the amount of air from the air dryer 1431. the flow meter 1432 and the first flow divider 1413 are connected to the second flow divider 1433 while the second flow divider 1433 is further connected to the heater 1434 by a pipe.

The first flow divider 1413 and the heater 1434 are connected to the control valve 144, while the control valve 144 is further connected to the air channel 1426.

Thus, when the mold module 142 is assembled, the high-pressure gas from the control valve 141 is guided to flow into the second flow divider 1433 by the use of the first flow divider 1413, and at the same time, the gas from the flow meter 1432 flows into the second flow divider 1433, so that the high-pressure gas is mixed with the gas from the flow meter 1432 into a high-temperature high-pressure gas. Thereafter, the high-temperature high-pressure gas is guided to flow into the control valve 144, where by the control of the control valve 144, the high-temperature high-pressure gas is further being guided to flow into the cavity 1422 for heating the same.

Moreover, the gas from the flow meter 1432 that is being guided to flow into the second flow divider 1433 can further be heated by the heater 1434, and then the heated gas is controlled by the control valve 144 to flow into the cavity 1422 via the air channel 1426 for heating the cavity 1422.

In a condition when there are melted flow inside the cavity 1422, the high-pressure gas from the first flow divider 1413 that is guided to flow into the control valve 144 and thus being controlled thereby can be guided to flow into the cavity 1422 via the air channel 1426 so as to be used as the counter gas. It is noted the pressure of the counter gas is ranged between 1˜300 bar, but is not limited thereby.

Please refer to FIG. 3, which is a schematic diagram showing steps perform in a method for metal injection and counter pressure according to an embodiment of the present invention. As shown in FIG. 3, the method for metal injection and counter pressure comprises the following steps:

-   -   Step S1: particles are provided, whereas the providing of the         particles further comprises a step selected from the group         consisting of: using a mixing unit 10 to mix particles with         metal powder and a binding agent in a predetermined ratio so as         to form a mixture, and then providing the mixture to a blending         unit 11 to be blended into a blend, and then providing the blend         to a pulverizing unit 12 to be pulverized into a powder, and         then providing the powder to a granulation unit 13 to be         granulated into the particles; and using a particle providing         assembly 17 to apply a mixing process, a blending process, a         pulverizing process and a granulation process upon particles         with metal powder and a binding agent so as to transforming the         mixture of the particles with metal powder and the binding agent         into the particles; in that the blending of the mixture is         performed at a preset blending temperature ranged between 180°         C.˜220° C., while the preferred temperature is 190° C., 195° C.         or 200° C.;     -   Step S2: a green part is molded in a manner that the particles         are fed into a melting module 140 for melting the particles into         a melted flow that is guided to flow into a mold module 142         while having a counter pressure module 141 to apply a counter         gas with a predetermined pressure to the mold module 142 during         the molding of the green part; while the predetermined pressure         is ranged between 45 bar to 200 bar; and Step S3: the green part         is debinded and sintered in a manner that the green part is         provided to a debinding unit 15 for applying a debinding process         to the green part at a first preset temperature, whereas the         first preset temperature is ranged between 40° C.˜60° C., and is         preferred to be 45° C., 50° C. or 55° C.

In a condition when the binding agent is a compound composed of paraffin and a polymer material, the debinding of the green part is composed of a cold debinding procedure and a thermal debinding procedure that are designed to be performed sequentially one after another. The cold debinding procedure is performed first, in which the green part is soaked into a solvent for removing the paraffin from the green part, and then the thermal debinding procedure is performed by heating the green part at the first preset temperature for removing the polymer material from the green part.

However, in a condition when the binding agent used is a polymer material, the debinding of the green part is performed using an acid gas for removing the polymer material from the green part.

After debinding, the green part is provided to a sintering unit 16 for applying a sintering process to the green part at a second preset temperature so as to sinter the green part into an end product, whereas the second preset temperature is ranged between 1250° C.˜1500° C., and is preferred to be 1300° C., 1350° C., 1380° C., 1400° C. or 1450° C.

In an embodiment, a metal tensile test piece is used for illustration, whereas the metal tensile test piece is a 110.05 mm×23.05 mm×4 mm dog-bone type piece. After sintering, the shrinkage of the test piece is 15%.

Please refer to FIG. 4, which is a schematic diagram density of different green parts. In FIG. 4, curve A represents the density distribution of a green part at various locations (far, center, and near as referred to the entrance of the mold module 142), in a condition that there is no counter gas being applied to the melted flow in the mold module 142; curve B represents the density distribution of a green part at various locations (far, center, and near as referred to the entrance of the mold module 142), in a condition that there is a counter gas of 50 bar being applied to the melted flow in the mold module 142; and curve C represents the density distribution of a green part at various locations (far, center, and near as referred to the entrance of the mold module 142), in a condition that there is a counter gas of 100 bar being applied to the melted flow in the mold module 142 during the solidification the melted flow into the green part.

As shown in FIG. 4, the lager the counter gas pressure is, the larger the density of the green part will be; and vice versa.

Please refer to FIG. 5 is a schematic diagram density of different green parts after debinding. In FIG. 5, curve D represents the density distribution of a curve-A green part after debinding at a near, a center and a far locations; curve E represents the density distribution of a curve-B green part after debinding at a near, a center and a far locations; and curve F represents the density distribution of a curve-C green part after debinding at a near, a center and a far locations.

As shown in FIG. 5, the lager the counter gas pressure is, the larger the density of the green part will be; and vice versa.

Please refer to FIG. 6, which is a schematic diagram density of different debinded green parts after sintering. In FIG. 6, curve G represents the density distribution of a curve-D green part after sintering at a near, a center and a far locations; curve H represents the density distribution of a curve-E green part after sintering at a near, a center and a far locations; and curve I represents the density distribution of a curve-F green part after debinding at a near, a center and a far locations.

As shown in FIG. 6, the lager the counter gas pressure is, the larger the density of the green part will be; and vice versa.

To sum up, during the molding of the green part by the use of the system and method of the present invention, the density of the green part is increased when there is a counter gas with the predetermined pressure being applied to the green part. In addition, not only the feedstock is compacted by the pressure of the counter gas and thus the tensile strength is enhanced, but also the metal powders in the feedstock is enabled to be distributed uniformly so that the uneven shrinkage problem caused during sintering is improved.

With respect to the above description then, it is to be realized that the optimum dimensional relationships for the parts of the invention, to include variations in size, materials, shape, form, function and manner of operation, assembly and use, are deemed readily apparent and obvious to one skilled in the art, and all equivalent relationships to those illustrated in the drawings and described in the specification are intended to be encompassed by the present invention. 

What is claimed is:
 1. A method for metal injection and counter pressure, comprising the steps of: providing particles; and enabling a green part to be molded in a manner that the particles are fed into a melting module for melting the particles into a melted flow that is guided to flow into a mold module while having a counter pressure module to apply a counter gas with a predetermined pressure to the mold module during the molding of the green part.
 2. The method of claim 1, wherein the predetermined pressure is ranged between 45 bar and 200 bar.
 3. The method of claim 1, wherein the providing of the particles further comprises a step selected from the group consisting of: using a particle providing assembly to apply a mixing process, a blending process, a pulverizing process and a granulation process upon particles with metal powder and a binding agent so as to transforming the mixture of the particles with metal powder and the binding agent into the particles; and using a mixing unit to mix particles with metal powder and a binding agent to form a mixture, and then providing the mixture to a blending unit to be blended into a blend, and then providing the blend to a pulverizing unit to be pulverized into a powder, and then providing the powder to a granulation unit to be granulated into the particles.
 4. The method of claim 3, wherein the mixing unit is operated at 180° C. to 220° C. to mix particles with metal powder.
 5. The method of claim 1, further comprising the steps of: providing the green part to a debinding unit for applying a debinding process to the green part at a first preset temperature; and providing the green part after debinding to a sintering unit for applying a sintering process to the green part at a second preset temperature so as to sinter the green part into an end product.
 6. The method of claim 5, wherein the first preset temperature is between 40° C. and 60° C.
 7. The method of claim 5, wherein the debinding of the green part is composed in sequence of a cold debinding procedure and a thermal debinding procedure; and wherein when the binding agent is a polymer material, the debinding of the green part is performed with an acid gas for removing the polymer material from the green part.
 8. The method of claim 1, wherein the particles comprises metal powder and a binding agent, the binding agent comprises paraffin and a polymer material, the metal particle is 50% to 70%, the polymer material is 19% to 29%, and the paraffin is 11% to 21%. 